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From: doug@eris.berkeley.edu (Doug Merritt)
Newsgroups: comp.dsp
Subject: Re: Autocorrelation Pitch Tracker
Message-ID: <1991Apr13.013025.26614@agate.berkeley.edu>
Date: 13 Apr 91 01:30:25 GMT
References: <78395@bu.edu.bu.edu> <1991Apr6.062906.11886@cs.cmu.edu> <51258@apple.Apple.COM>
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In article <51258@apple.Apple.COM> malcolm@Apple.COM (Malcolm Slaney) writes:
>That said, you need more than two cycles of a signal to perceive its pitch!
>I just tried it.  I synthesized (with MatLab) a signal that looks like
>	1 second of silence 
>	a small number of cycles of 220Hz sine wave
>	1 second of silence
>If there is only one or two cycles then all one hears is a click.  There is
>nothing in this sound that would let me hear a pitch.  Not until I get to 
>four or five cycles does it start to sound musical so I can assign a pitch
>to it.  Try it, if you don't believe me.

This is an interesting subject. I have to wonder whether your experiment
might be faulty, though. What if you're simply uncovering funny behavior
in your sound system rather than in your ear, for instance? I think for
something like this you'd want to verify that the sound you intended is
really being created; try a mike & a digitizer to bring it back into your
system.

Besides all that, consider the Fourier domain of this. My intuition
is flakey here, but it seems to me that since the period of the boxcar
window is almost equal to the period of the sine, the effect in the Fourier
domain should be almost identical to a single pulse of a square wave in
the first place, no? Hence a click.
	Doug
-- 
--
Doug Merritt		doug@eris.berkeley.edu (ucbvax!eris!doug)
		or	uunet.uu.net!crossck!dougm